Heating device with enclosed combustion chamber



May 24, 1955 HUBER ETAL HEATING DEVICE WITH ENCLOSED COMBUS'ITION CHAMBER Filed March 31, 1953 2 Sheets-Sheet l @MM WJQMTM ATTORNEYS 2 Sheets-Sheet 2 man 2 May 24, 1955 HUBER ETAL 'HEATING DEVICE WITH ENCLOSED coMBUsToN CHAMBER Filed March 31, 1953 .5, "lu s .1U i, la 55.5

////l f/ /f// nted States Patent C HEATING DEVICE WITH ENCLOSED COMBUSTION CHAMBER Ludwig Huber, Uberlingen am Boden, and Bodo Lafferentz, Nussdorf, near Uberlingen am Boden, Germany, assignors, by mesne assignments, to Swingfre (Bahamas) Limited, Nassau, Bahamas, a corporation of the Bahamas Application March 31, 1953, Serial No. 345,854 Claims priority, application Germany April 5, 1952 6 Claims. (Cl. 126--91) This invention relates to heating devices in which fuel is burned within a closed combustion chamber and which serve forV heating working or residential rooms for human occupancy.

The invention particularly concerns heating devices of the type described, in which a superatmospheric ressure in excess of the heated room air pressure is produced lin the combustion chamber during operation. The gases of combustion in the combustion chamber and the exhaust carrying heating ducts are accordingly under a certain superatmospheric pressure.

An object of the present invention is to provide a heating device in which the escape of combustion or exhaust gases into the heated room is positively prevented despite the fact that these gases are under superatmospheric pressure in the heat dissipating ducts and chambers of the device.

A particular object of the invention is the provision of a heating device, the air heating surfaces of which are indirectly heated by the combustion gases, but in which the combustion chamber and the exhaust gas ducts are in such good heat conducting contact With such surfaces that the air heating surfaces reach their desired operating temperatures within a very short interval after combustion is initiated. Another object of the invention is the provision of a heating device which permits the production of surprisingly large amounts of heat within a very small space, and which is for this reason especially suitable for use as a portable heater.

The invention is generally characterized by the provision of a closed air-tight safety chamber in which is enclosed the combustion chamber and the part of the exhaust gas duct which serves to give E heat. This safety chamber is connected to a reduced pressure zone of the burner through a suction duct. The reduced pressure zone may be readily obtained in constant pressure burners by passing the fuel or the forced-in combustion air across an iniector or a venturi, in which case the suction duct is connected to the reduced pressure zone of the injector or venturi. Even more favorable operation may be obtained when the combustion device is a resonant pulse jet device, that is, a burner in whose acoustically tuned combustion chamber and exhaust duct are produced periodic detonations at the natural frequency of such chamber and duct. In such a burner, there occur, between individual pressure phases or pulses resulting from the detonations, temporary short intervals when there is a considerably reduced pressure in the combustion chamber. These periods of reduced pressure, or suction phases of operation, are usually employed in resonant pulse jet burners for drawing in a fresh charge of combustion mixture. It is proposed, in accordance with the present invention, to connect the suction duct of the safety chamber through a check 2,708,926 Patented May 24, 1955 valve with the combustion chamber and exhaust duct system in order to obtain an approximately constant reduced pressure in the safety chamber connected with the suction duct. It is preferred to use as this check valve, the suction check valve of the resonant pulse jet burner itself by connecting the safety chamber suction line between this check valve and the conventional suction silencer of the burner air suction line.

By using the described safety chamber, which is airtight and is connected through a suction duct with a reduced pressure zone of the burner, we positively insure that any gases which may escape through possible leaks in the combustion chamber or in the exhaust gas ducts which serve for heating are immediately sucked back into the burner and, therefore, cannot enter the heated rooms. The use of a resonant pulse jet burner provides the additional advantage that any leaking waste gases which are returned to the burner air intake interfere with the periodic detonation of fuel in the burner and, after a short time, cause the resonant combustion to die out. Thus, such a device automatically discontinues its operation if leaks occur.

In describing the invention in detail, reference will be made to the accompanying drawings, in which certain embodiments thereof are illustrated.

In the drawings:

Fig. l is a side elevation, partly in section, of a heating device embodying the invention;

Fig. 2 is a sectional elevation, taken along the line 2 2 of Fig. 1 and viewed in the direction of the arrows;

Fig. 3 is an enlarged partial sectional elevation of the burner of the device shown in Fig. l; and

Fig. 4 is a side elevation, partly in section, of a heating device embodying the invention and incorporating a modified burner.

The heating device shown in Figs. l, 2 and 3 includes an air-tight closed metal casing or shell 1 having a top cover plate 1a and carried by feet 2. The sheet metal walls of the casing serve to radiate the heat produced to the surrounding room. Within the shell 1 is located a combustion chamber 3 into which air and fuel flow in the direction of the arrow A1 and from which the hot exhaust gases are forced to the exhaust 5 through the serpentine duct 4. Since the exhaust gases, while passing through the exhaust duct 4, cool down to about C. (212 F.), they can be discharged from the exhaust 5 in the direction of the arrow Azthrough a conventional hose (not shown) into the outer atmosphere. The safety chamber 6, which is enclosed airtight by the shell 1, is located between the combustion chamber and exhaust duct gas conducting system 3, 4, and the atmosphere of the heated room. The heat transfer from the walls of the combustion gas conducting system 3, 4 to the walls of the shell l takes place partially by radiation and partially by conduction. In order to increase the portion of heat transferred by conduction, there are inserted in and welded to the shell 1 and its top plate 1a a plurality of tins 7, and the combustion chamber 3 and exhaust duct 4 are fitted into cut-out recesses in these tins, as shown in Fig. 2, so that the fins also serve as supports for the duct 4. In order to further increase the heat transfer to the outside, the safety chamber 6 may be completely or partly filled with metal wool or shavings, and we have illustrated this by showing a packing 8 of metal wool, such as aluminum wool, within the chamber 6. lf an increased heat transfer is desired, the metal packing may be replaced wholly or in part by minerals, such as coarse grained pumice, it being necessary, however, that the packing used contain a suiiiciently large and communieating volume of air so that the chamber' can be put under sub-atmospheric pressure.

As will be seen from Fig. 3, the outlet pipe 9 of a blower 10 discharges into the combustion chamber 3. The blower 10 is located in a casing 11 and is driven by a small electric motor 12. The discharge from the blower charges the combustion chamber 3 with combustion air. Between the outlet pipe 9 and the combustion chamber 3 there is located a venturi throat 13 into which a fuel nozzle 14 empties. 1n the wall of the passage surrounding the venturi throat 13 is located an annular ring channel 1S which is connected with the reduced pressure zone of the Venturi throat by a number of radial ducts, as shown, and is connected also to a suction duct 16. As shown in Fig. l, this suction duct 16 has at its upper end an air filter 17 located within the closed shell 1. The Safety chamber 6 is thus connected through the suction duct 1 6 to the decreased pressure prevailing in the venturi throat 13, and the filter 17 prevents dust or other foreign matter from entering into the duct 16 or the channel 15.

The fuel nozzle 14 is connected with a fuel tank 19 (Fig. l) through a calibrated fuel pipe 18. The reduced pressure in the safety chamber 6 is maintained so long as the blower 10 is operating. lf the drive of the blower 1t) is interrupted, no further fuel is drawn in and the combustion stops.

A glow plug 20 is provided for igniting the flame, and its glow coil 20 is heated by current from a transformer 21, the secondary of which also energizes the motor 12 so that the glow plug coil 20' is always glowing when the motor 12 is energized. With this arrangement, the entire heating device can be switched on and off by a switch 22 that controls the energization of the primary winding of the transformer 21. In order to effect automatic deenergization of the device in the event of an empty fuel tank, there may be provided in the fuel tank 19 a float controlled contact connected in series with the switch 22 which will interrupt the energizing circuits ofthe motor 12 and the transformer 21 as soon as the fuel level in the tank 19 drops to a predetermined point.

A resonant pulse jet combustion device has been found even more favorable than a constant pressure burner as a source of heat for heating devices embodying the invention. The pulse jet combustion device may desirably take the form illustrated in Fig. 4.

A combustion mixture is supplied to a combustion chamber 3a from a mixing tube 2S in the axis of which a glow plug 26 is located and into which open both a:

the fuel feed nozzle of a carburetor 26a and the chamber of a check valve 27. The combustion chamber 3a forms, with the exhaust duct 2S, a Helmholtz resonator which is set in vibration by the detonation of the first charge of combustion mixture and thereafter detonates periodically at its natural frequency, alternately drawing in a combustion mixture of fuel and air and causing the latter to detonate. A resonant pulse jet combustion device of this type is shown and described, for example, in the pending application of Franz A. Haag, Serial No. 304,581, filed August 15, 1952, and assigned to the assignee of this application.

The exhaust duct 28 empties into a mufiler 29 which is divided into several differently tuned resonators which act as acoustic filters by means of baffles 30 and 31. For the purpose of stabilizing the vibration of the burner 3a and exhaust duct 28, the first resonator into which the duct 28 empties has approximately the same resonant frequency as that of the chamber and duct 3a, 28. This arrangement for silencing the exhaust of the resonant jet pulse combustion device is described more in detail in the copending application of Franz A. Haag, Serial No. 319,300, filed November 7, 1952, and assigned to the assignee of this application.

The combustion chamber 3a is enclosed within one end of the muffler 29, so that the combustion chamber attains a relatively high temperature, which makes it possible to prevent any carbon accumulation within the combustion chamber even when burning diesel oil or like low volatile fuels.

A waste gas duct 4a is connected to the muffler 29 and passes in serpentine form within the shell 1a forming the safety chamber and is finally connected through such shell to the outside atmosphere.

The check valve 27 of the burner is connected with a suction air filter 33 through a suction mufer 32. The suction muffler 32 is divided by baffles 34 and 35 into a plurality of differently tuned resonators which together act as an acoustic filter.

The safety chamber 6a is preferably filled with a porous packing 8a of high heat conducting capacity, such as that described above in connection with the modification of Fig. 1. The packing 8a also serves as a silencer for the operation of the device.

After the resonant pulse jet combustion device has been set in operation in a manner described in the aboveidentified applications, that is, by electrically heating the coil of the glow plug 26 and forcing in air by means of an air pump (not shown), there is drawn in through the check valve 27, in phase with the vibrating combustion operation, air to support combustion, and this results in a drop in pressure to a sub-atmospheric value between the air filter 3 and the check valve 27, thus forming a zone of reduced pressure (about 10 to 30 mm. of water) in front of the check valve. This reduced pressure is connected through a suction tube 16a and an air filter 17a to the inside 6a of the shell 1, which is air-tight.

If leaks appear in the combustion and exhaust duct system 3a, 28, in the muffler 29, or in the waste gas duct Sa, so that exhaust gases enter the safety chamber 6a,

such gases are drawn through the filter 17a, the suction tube 16a and the check valve 27 directly into the mixing tube 25 of the combustion chamber 3a. This results in choking and so terminating operation of the burner by its own exhaust gases, with the result that the pulsating detonations stop and no further fuel is drawn from the carburetor 26. Thus, the heating device turns itself off automatically upon the appearance of waste gases within the safety chamber which indicates a dangerous leakage or failure of the apparatus.

We claim:

1. A heating device comprising a burner having a combustion chamber, an air intake passageway leading to said combustion chamber, means for introducing fuel into said air passageway to form a combustible mixture, means providing a zone of sub-atmospheric pressure in said air-intake passageway during operation of the burner, a combustion gas conduit extending from said cornbustion chamber and adapted to connect with an exhaust means, a substantially air-tight casing enclosing and forming a safety chamber around a major portion of said combustion-gas conduit, and a suction duct connecting the sub-atmospheric pressure zone of the burner to said safety chamber, said casing being sealed to exclude admission of air thereto during operation of the burner, whereby during operation of the burner suction is applied to the space within said safety chamber.

2. A heating device according to claim l, in which the burner is a constant pressure burner having means for forcing combustion air through said intake passageway to the combustion chamber, and a constriction is provided in the air passageway to form the zone of subatmospheric pressure.

3. A heating device according to claim 1, in which the burner is a resonant pulse jet combustion device having the air intake passageway connected to the combustion chamber through a check valve, and in which the combustion gas conduit is under super-atmospheric pressure during at least a part of the time that the burner is in operation.

2, Rfos, 92a

4, A heating device according to claim 1, in which an air lter is lprovided in the suction duct.

5. A heating device according to claim 1, in which heat conducting means are provided in the safety chamber in contact with both the outer surfaces of the combustion gas carrying system and the casing walls.

6. A heating device according to claim 5, in which at least a part of the heat conducting means comprises a porous packing material.

References Cited in the le of this patent UNITED STATES PATENTS OBrien Feb. 22, 1887 Junkers Oct. 6, 1931 McCollum Jan. 28, 1947 Feuerle Apr. 18, 1950 Kamm et al June 23, 1953 

